New external C5 FPR in '98 F-body, high fuel pressure whacking fuel trims

[JimMueller]

Long story short, the metal tank in my '98 Camaro developed a small leak which we couldn't locate. Plus, the complete 255LPH fuel sender kit I bought from a vendor didn't include the plastic bucket, so I had bad starvation issues. So, a few days ago, I had a shop install a used ;99-'02 plastic tank, a new 340LPH sender kit (excluded internal regulator) and the external C5 fuel filter/regulator (WIX 33100) conversion. My MAF & VE adjustments were already very close when using the 255LPH, internal tank regulator, and external filter.

I logged the first cold start and first warm start after completing the install while looking for leaks. Both times, fuel pressure started between 80-90PSI, then dropped to a solid 58PSI within 2 minutes.

As part of rebuilding my gauge output & primary tank volume tables, I took the car for a long drive yesterday.
* The first log from that trip shows it took 27min for the pressure to drop to 60PSI from a cold start, then remained at a solid 57-60PSI the remainder of the log (1h15min). LTFTs in this log were generally -4 to 4.
* The second log from that trip was after adding some fuel to the tank. When merging on to the county highway, it stumbled a bit when accelerating. I noticed the fuel trims were very rich and I had also forgot to add a PID to my display. I forgot to save this log when adding the PID.
* The third log, a warm start began with 56-60PSI and remained there the remainder of the log (30min). However, most of my LTFT's were -10 to -15 in that log.

If the high pressure was limited to the first minute or so, I wouldn't be so irked; I'm going to try to some replacement regulators. From the tuning and drivability perspective, which is the best way to address this behavior before the physical problem is resolved, or if a replacement regulator doesn't improve the situation? Disable LTFT's? Disable CL?

Thanks guys!

[blindsquirrel]

The Corvette filter/regulator can't flow enough volume through the return orifice for that pump.

[blindsquirrel]

Many tales of woe: https://www.google.com/search?tbs=li...orvette-filter

[blindsquirrel]

Is there a reason you can't reinstall the in-tank regulator? All that will do is add a second path for the return fuel to take, the system pressure will be set by whichever of the two regs in parallel has the lowest set pressure.

[JimMueller]

I reviewed all the search results in your link. Does the 1998 PCM allow this tuning workaround?

I had a similar problem with my pump overpowering the vette regulator/filter. Was showing varrying fuel pressure from 70 psi at idle to 62 psi under load. I ended up tunning around it by chaging my min/max fuel pressure and adjusting the flow rate table by calculating injector flow rate per fuel psi. I used a stock 08 vette tune with my swap that had a 58 psi flow rate across the board, which is what the vette regulator should be governing to. My situation is more complicated then yours, as i swapped an l92 escalade motor into a stick shift car. Used the vette tune as a base and had to retune ve and maf, as they were way off due to the different cam profiles. Your swap sounds like a simple plug and play with the ls3 crate. Easiest fix would probably be to just install a regulator on the rail and ditch the other one, if fuel pressure is indeed the problem.

Obviously the 1998 fuel system is returnless; you commented in another thread... so it sounds like changing it to return style adds more grief.

A return style regulator makes it way more complicated, lots of stuff in the tune has to be changed. For a setup like this all you need is a fixed, stable, correct 58psi supply. Easiest fix is a pump that isn't mismatched with what the rest of the combo needs - second easiest is a NON-REFERENCED regulator mounted in the rear that simply dumps anything over 58psi back into the tank.

It sounds as if my solutions are:
1) Replace the 320LPH pump in the bucket with a 255LPH pump (Although I'd prefer a 320 over a 255 for growth)
2) Add something like an Aeromotive EFI 13101 between the C5 FPR and the tank, and swap the C5 FPR with a normal non-FPR inline filter. It looks a little large to fit in the OEM F-body location though.
3) Hope that the remainder of the return system between the aftermarket regulator and the tank is adequately sized as well, else need to replace those lines as well.

[JimMueller]

Is there a reason you can't reinstall the in-tank regulator? All that will do is add a second path for the return fuel to take, the system pressure will be set by whichever of the two regs in parallel has the lowest set pressure.

The kit I purchased was intended for use with an external FPR, so they intentionally excluded an internal FPR. They recommended the C5 FPR or an aftermarket FPR in conjenction with the pump kit. Because the C5 FPR was more plug'n'play, I chose that solution. I do not know what would be involved in adding an internal FPR to the bucket.

I'd rather not pay a lot more labor to drop the tank again to swap the pump and/or add an internal FPR. I don't want to add additional variables into the equation. I've read some others on ls1tech.com (at least temporarrily) resolved their issue by replacing the C5 FPR they received with another stock replacement (Wix 33100 or ACDelco GF845). Baed upon what I've read here, I'm not confident that will be a long-term solution, which would then lead me to the atermarket FPR solution.

[JimMueller]

What type of anomalies should I expect when driving the vehicle in this condition? What type of behaviors can I change to mitigate the situation until it is solved?

[blindsquirrel]

There is no physical fuel pressure sensor on any of these systems, so the PCM will have no way to know whether the rail pressure is changing or not. Injector data set up for a returnless system assumes a stable, fixed rail pressure. Injector data can be easily changed to suit a referenced regulator, all that does is stop the PCM from adjusting the flow rate as manifold pressure changes. There are no settings you can use to make it work with both a variable rail pressure and also adjust flow based on manifold pressure. Not both at the same time.

I would think that if you have an internally-regulated pump module that's been specced for use with an external regulator that they would have just pulled the internal regulator out of the hanger and replaced it with a plug. Unlikely they would have built a whole new pump module just to eliminate the spot where the original regulator went. I don't see why you couldn't pull the block-off plug and put a stock regulator back in its place.

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